# std::discrete_distribution

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< cpp‎ | numeric‎ | random

Defined in header `<random>` |  |
template< class IntType = int > class discrete_distribution; |  | (since C++11)

`std::discrete_distribution` produces random integers on the interval `[`​0​`,` n`)`, where the probability of each individual integer `i` is defined as wi/S, that is the weight of the `i`th integer divided by the sum of all `n` weights.

`std::discrete_distribution` satisfies all requirements of RandomNumberDistribution.

### Template parameters

IntType | - | The result type generated by the generator. The effect is undefined if this is not one of short, int, long, long long, unsigned short, unsigned int, unsigned long, or unsigned long long.

### Member types

Member type | Definition
`result_type` (C++11) | IntType
`param_type` (C++11) | the type of the parameter set, see RandomNumberDistribution.

### Member functions

(constructor) (C++11) | constructs new distribution (public member function)
reset (C++11) | resets the internal state of the distribution (public member function)
##### Generation
operator() (C++11) | generates the next random number in the distribution (public member function)
##### Characteristics
probabilities | obtains the list of probabilities (public member function)
param (C++11) | gets or sets the distribution parameter object (public member function)
min (C++11) | returns the minimum potentially generated value (public member function)
max (C++11) | returns the maximum potentially generated value (public member function)

### Non-member functions

operator==operator!= (C++11)(C++11)(removed in C++20) | compares two distribution objects (function)
operator<<operator>> (C++11) | performs stream input and output on pseudo-random number distribution (function template)

### Example

Run this code

    #include <iomanip>
    #include <iostream>
    #include <map>
    #include <random>

    int main()
    {
        std::random_device rd;
        std::mt19937 gen(rd());
        std::discrete_distribution<> d({40, 10, 10, 40});
        std::map<int, int> map;

        for (int n = 0; n < 1e4; ++n)
            ++map[d(gen)];

        for (const auto& [num, count] : map)
            std::cout << num << " generated " << std::setw(4) << count << " times\n";
    }

Possible output:

    0 generated 4037 times
    1 generated  962 times
    2 generated 1030 times
    3 generated 3971 times

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